Saturday, June 27, 2009

The Rottweiler Returns – Atmospheric Correction???

“The views expressed are those of the author and do not necessarily represent those of the National Weather Service.”

Time constraints (and scientific/efficiency considerations) continue dictate for these discussions to be scaled back. The 6 June posting has relevant links, and there is no need to be redundant.

Short and simple, starting in March and “maturing” during April and May, the global ocean-land-atmosphere dynamical system has shifted toward a weak El-Nino base state. The phase space plots depicting the WH (2004) measure of the MJO and WB (2009) measure of the GWO clearly show this. That is, a general displacement toward octants 7-8. The GWO projection has been “weaker” because of complicated issues involving the dynamics of the earth-atmosphere AAM budget including zonal mean contributions. Remember that the WB (2009) GWO is a global dynamical measure of the circulation as opposed to the empirical and equatorially confined WH (2004) MJO.

SST anomalies across the entire equatorial Pacific Ocean basin including the Nino regions are positive, including ~plus 1C and greater east of 160W. Further, the 29C isotherm is well to the east of the Dateline (see TAO and other plots). However, the subsurface anomalies across the west Pacific are not that robust, only ~plus 1-2C down to around 200m. In any case, this basin-wide warming of the Nino SSTs is a response to the global circulation (more said below), and our weak El-Nino is already (and has been) impacting global weather including the USA. Additionally, as discussed previously, the evolution to get to where we are at (in phase space) has been impacting global weather since December 2008 (recall the GWO driven “cheap” MJOs).

My “punch line” for today is that, in general, the global circulation, as part of a complex forcing-response-feedback “loop”, has been leading the SSTs since about boreal autumn 2006 (see previous posts). The latter includes projections on the “beloved” ONI and other measures such as the PDO. I am concerned this is still going on, perhaps working with the seasonal and annual cycles (there are reasons).

Since about mid-May, anomalous zonal mean westerly wind flows have been shifting off the equator into the subtropical and midlatitude atmospheres, with the largest magnitudes across the winter Southern Hemisphere (greater than 10m/s at 200mb). Frictional dissipation due to interactions with tropical forcing (including a recent weak MJO; e.g., WWBs) and midlatitude eddies led to a strong negative global frictional torque by mid-June. Updated through 24 June the there is a clustered negative global mountain torque of roughly minus 20 Hadleys. The point is this is an example of a negative global friction-mountain torque index cycle linked to atmospheric processes including tropical forcing (GWO 8-1). Global relative AAM has decreased to near the R1 data climatology, and tropical convection has become re-established ~10N/90E, good news for the Indian monsoon system. Will this tropical forcing coherently propagate into the west Pacific Ocean during the next few weeks? Stay tuned.

Like the recent behavior of the financial markets, we have seen an “AAM correction”. However, is this simply a subseasonal variation destructively interfering with El-Nino, or is a process beginning that not only could weaken EL-Nino this upcoming boreal autumn, but perhaps bring a La-Nina situation boreal winter 2009-10? The answer is unclear, and careful daily rigorous monitoring is critical. Hopefully at some point the atmosphere and the financial markets will become decoupled!

Animations of upper tropospheric daily mean vector wind fields do show that anomalous subtropical and midlatitude ridges have returned (bearish). Loosely, phases 1-2 of the both the MJO and GWO 250mb psi composite anomaly plots represent the global atmosphere. Responding to the weakening of the North Pacific Ocean jet, the warm ridge in place across the south central and southeastern states last week is retrograding. That behavior is consistent with a brief excursion toward phases 3-5. However, with low confidence, I think another loop in GWO/MJO phase spaces displaced toward octants 7-8-1 is probable during the next 1-3 weeks. As seen from the snr composites, temperature anomalies across the lower 48 states are very sensitive in this region of phase space (as is numerical model predictability skill). My own thought is the intense heat may be focused across the south central states the rest of this summer, with increasing probabilities of northeastward expansions during August. I will try to write a short posting 3 July.

The latest MJO ensemble forecast shows a strong MJO amplifying in octant 1 about a week from now. If that really happens, it might be time to start having serious doubts about the future of this El Nino.

I do agree about the reality issues of our El-Nino. We may observing a case where stochastic forcing giveth.... Remember that there are serious predictability issues in this region of phase space. Also, not all EPS support the NCEP rendition.

In any case, tropical forcing is starting to "sputter" over the WPAC, and there is some evidence of the loop I discussed. Our weak El-Nino is probable to have global impacts the rest of this summer. There may be a tendency to start hanging out in octants 8-1-2 of MJO/GWO phase spaces. The "truth" of this El-Nino is likely to be exposed ~OND. Right now, the future time evolution of ENSO is unclear.

A no show El-Nino would be something. The latest El-Nino rally was one of the strongest that many have seen. It would be unfortunate if there isn't to be an El-Nino for DJF considering many had high hopes for a good winter. I was hoping for a west based Nino, but I would take neutral ENSO just as much.

An MJO 8-1-2 Winter would be intense in the east. Could it be that those wanting a late 1970's winter may not need an El Nino? That phase space would certainly allow for ample blocking possibilities (given some extratropical cooperation).

Do you think the strong high pressure being forecast by both the ECMWF and GFS over the north central and northeast Pacific is a bad sign for the El Nino? In my way of thinking a massive surface high pressure complex over that region should result in strong trades along the bottom of the high pressure. I am also seeing some very nice symmetry in the pressure fields being progged north and south of the equator.

It is interesting to note how the West Coast SST's have reacted to the pattern shift that occured around mid month. The SST's had dramatically risen to above normal in the first half of June and have since dropped back to slightly below normal in many places, thanks to the return of brisk NW surface winds along the West Coast. The patterns in early June were very consistent with a developing El Nino, but now they don't appear to be.

I remember during the last significant El Nino event which was in '97, upwelling pretty much sputtered along the west coast with upwelling and downwelling depending on the weather pattern until late August/September, then things really warmed SST wise thereafter along the US west coast. While I don't want to suggest this possible El Nino will be nearly as significant as that at all, the overall circulation of the atmosphere seems similar at least for the west coast for now. What looks promising for now is the continued deep re-appearing troughy pattern along the west coast so far. Maybe I might be wrong but this may help the west coast get out of the dry pattern we have been in for the last three years south of the Oregon border.

According to the re-analysis maps from 1997, the West Coast SST's were persistently warm in the late spring and summer of 1997. Besides that the El Nino was already in full swing by this time.

I would also consider 2002-03 to be a pretty significant warm ENSO event.

I would consider the current pattern for the Pacific NW to be very much in line with the last two summers. Unusually chilly nights have returned to windsheltered / outlying areas. Similar cool nights alternating with brief heatwaves were common the past couple of summers.

Thank you for the good discussion and comments. I refer to a bullish (bearish)atmosphere when AAM is trending upward (downward) consistent with what is probable during an evolution toward El-Nino (La-Nina). Wall Street today was La-Nina like. I draw the analogy between AAM and its time tendency with the financial markets for fun as well as to help communicate.

In short, the weather-climate dynamical system is nothing like 1997-98. In fact, the global circulation has been bearish for the last few weeks. That includes decreasing AAM, anomalous midlatitude ridges, and IO forcing dominating the WPAC. The ENSO situation for the upcoming boreal winter is unclear.

I am no Ed Berry, but I have some idea of what they were saying on the Weather channel. At present there is a high pressure ridge off the West Coast which has caused a trough to settle into the SW (responsible for the cool June in the SW). In return that trough is forcing a ridge from hell over the South Central United States. Finally the South Central ridge is forcing a trough over the Northeastern states. This is all part of how atmospheric features teleconnect across the entire Northern Hemisphere.

I believe Ed mentioned he thinks the current South Central heat wave will eventually migrate into the Northeast. Once their trough moves out that would seem pretty likely.

Jim is correct about the anomalous and persistent trough-ridge-trough that is directly linked to GWO 8-1. In fact, during much of this past winter the La-Nina base state contributed to anomalous ridging across the south central states. Ironically, considering seasonal cycle issues, even though the global atmosphere went away from La-Nina, ridging actually intensified across your region during June. That shows you how random some of these large climate anomalies can be.

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